The known spermicidal agents, nonoxynol-9 and gramicidin, exert their effects via a detergent-like ability to damage the sperm plasma membrane, perturb its conformation and destroy its semi-permeable nature thereby impairing the sperm motility and egg fertilizing functions (Wilborn, et al., Fertil Steril 1983; 39:717-719; Bourinbaiar, et al., Life Sci 1994; 54:PL 5-9). Because of their non-specific membrane disruptive properties, such vaginal spermicides have been shown to damage the cervicovaginal epithelium, as well, which may lead to a lower degree of protection from sexually transmitted diseases (Niruthisard, et al., Sex Transm Dis 1991; 18:176-179). A novel vaginal contraceptive preferably does not function with the non-specific membrane toxicity mediated by detergent-type action of the currently available vaginal contraceptives.
Vanadium is a physiologically essential element which can be found in one of five (I to V) oxidation states. Several inorganic salts containing vanadium with oxidation state +4 (IV) have been shown to function as modulators of cellular redox potential and to exert pleiotropic effects in multiple biological systems by catalyzing the generation of reactive oxygen intermediates. See, for example, Shi, et al., Ann Clin Lab Sci 1996; 26:390-49; Byczkowski, et al., Bull Environ Contam Toxicol 1988; 41:696-703; Younes, et al., Toxicology 1991; 66:63-74, and Sakurai, et al., Biochem Biophys Res Commun 1995; 206:133-137. Reactive oxygen intermediates have been reported to affect sperm motility by a combination of peroxidation of membrane lipids and proteins (Aitken, et al., Biol Reprod 1989; 40:183-197; Jones, et al., Fertil Steril 1979; 31:531-537). Peroxidative damage to the sperm plasma membrane is an important pathophysiological mechanism in the onset of male infertility (Aitken, et al., BioEssays 1994; 16:259-267). It has also been shown that superoxide radicals generated by the action of xanthine oxidase exert a direct, suppressive effect on many aspects of sperm function (Aitken, et al., J. Reprod. Fertil. 1993; 97:441-450). Sperm are thought to be particularly susceptible to oxidative stress by virtue of their high content of unsaturated fatty acids and their relative paucity of cytoplasmic enzymes for scavenging the reactive oxygen intermediates that initiate lipid peroxidation (Alvarez, et al., J. Androl 1987; 8:338-348).
There is a need for new spermicidal compounds for contraceptive purposes. The ability of vanadium IV containing organometallic complexes to catalyze the generation of reactive oxygen species was evaluated for its potential to impact sperm activity. Results of studies with structurally distinct organometallic complexes containing vanadium (IV) surprisingly demonstrated these compounds to be potent spermicidal agents at nano-micromolar concentrations. These compounds have also surprisingly been found to exhibit selective apoptosis-inducing activity against testicular germ cells in vivo.